Radar is the technique of using radio waves to detect the existence of an object and then to find the object's position in relation to a known point. Air traffic control uses radar to track planes both on the ground and in the air, and also to guide planes in for smooth landings. Police use radar to detect the speed of passing motorists. The military uses it to detect an enemy and to guide weapons. NASA uses radar to map the Earth and other planets, to track satellites and space debris, and to help with docking and maneuvering of spacecrafts.
Radar systems typically operate by emitting, for example, microwave energy from a transmitting antenna in the form of a focused beam with known divergence angles. Some of this emitted microwave energy is reflected off objects in the beam's path and collected by a receiving antenna. This emitted and reflected energy is minimally affected by environmental conditions, such as in rain, fog, clouds, or time of day.
Continuous wave (CW) is one type of radar. CW relies on the “Doppler shift” in frequency to detect moving objects and to measure their speed. This phenomenon, known as the Doppler effect, occurs with radio waves as well as with sound waves. As an object approaches a radar antenna, the frequency of the signal reflected by the object is higher than that of the transmitted signal. Conversely if an object is moving directly away from the antenna the frequency of the reflected signal is lower than that of the transmitted signal. For stationary objects there is no change in the frequency of the reflected signal.
An improvement to CW radar is frequency-modulated continuous wave (FMCW) radar. FMCW radar utilizes a frequency-modulated waveform that is continuously transmitted from and received by a radar station. In FMCW radar, the time delay between an emitted wave from a transmitter and a reflected wave from the object is calculated at a receiver. The receiver then provides an indication of the range of the object.
FMCW radar not only measures range or distance to the object, but also the object's speed. The mixed signal holds information about the distance and velocity of the object. For example, the frequency of the oscillations in the mixed signal corresponds with the distance of the object. The difference between the up-slope and the down-slope of the mixed signal corresponds to the speed of the object. The amplitude of the oscillations of the mixed signal corresponds with the relative size or quality of the reflection.
Some existing sensors report the distance and speed of an object with some degree of accuracy, but require that a known object be targeted. Other sensors use a statically determined value for the amplitude to determine whether or not an object is in view.
There exists a need in the art for improved sensor systems.